There are a lot of crazy diet fads out there, and sometime in the future, when the technology is right, maybe there will be another: get in a time machine and tell your grandmothers to eat healthier food while they were pregnant with your parents. That is, if it turns out that the obesity in humans, like mice, can be affected by the diet of people two generations back.

So what’s the deal?
Scientists have shown that in mice, if a female eats a high-fat diet while she is pregnant and nursing, her offspring are larger and have a tendency to overeat. The really remarkable finding was that the second generation were also larger and were insulin insensitive.

What’s that?
Insulin insensitivity is a condition where the body is not able to respond normally to insulin. Insulin is produced after you eat, in order to signal your body to take up sugar from the blood and convert it into other types of energy. People who are insulin insensitive aren’t able to fully respond to this signal and have problems with their metabolism, such as abnormal blood sugar levels and weight gain. Insulin insensitivity is also associated with diabetes.

How is it possible that something that happened so long ago could have an effect?
Most people think that genes are the only thing we inherit from our parents and grandparents, but new research is showing that’s not the case. The sequence of your DNA is important for turning a gene on and off, but it isn’t the only thing that matters. DNA can also be modified by attaching small chemical groups to the backbone, without changing the sequence of the DNA. One example is that a methyl group can be attached to DNA and cause the gene encoded by that region of DNA to be silenced. This is called an epigenetic change, meaning that it is heritable but NOT caused by a difference in DNA sequence. The scientists conducting the study believe such a change is the root of the effect they are seeing.

How would that work?
Well, you could imagine that whatever a woman eats while she is pregnant and nursing could affect the baby, since the two of them are sharing nutrition. The nutrition that the baby is exposed to could lead to all sorts of changes, including epigenetic ones. Although they are still searching for the change that is responsible, scientists believe that it might be found in the hypothalamus, a part of the brain that controls behaviors related to food.

How would it work in the second generation? Who knows! Maybe it is behavioral – the original offspring are also more likely to overeat, so that might have an effect on their offspring. Or maybe there are also epigenetic changes in their reproductive cells (eggs and sperm), which will ultimately produce the next generation. Only time will tell!

Can human grandmothers have an influence over obesity also?
Nobody knows yet, but it’s going to be really important to figure it out. After all, we are in the midst of a huge obesity epidemic in America. If this effect is seen in humans, it would be really difficult for future generations to maintain a healthy weight with problems like a tendency to overeat and insulin insensitivity. Hopefully, scientists will be able to identify what is responsible for this effect, whether it is an epigenetic effect or something else, because then we will begin to understand exactly how and why it happens… and what we might be able to do about it.

THE BOTTOM LINE
Scientists have shown that in mice, some of the causes of obesity can be affected by the diet of mice two generations back. It’s not clear if this happens in humans, but if it does, it could mean even worse news for the obesity epidemic we’re currently seeing.